sfc: Move filter IDs to per-VLAN data structure

It is a step to support VLAN filtering in HW.
Until then, there is only one struct efx_ef10_filter_vlan per struct
efx_ef10_filter_table, with no VLAN information yet.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>